Apparatus for generating a passive movement of a patient in magnetic resonance tomograph

ABSTRACT

An apparatus for generating a passive movement of a patient in a magnetic resonance tomograph comprising a support ( 14, 17 ) for supporting at least one body part ( 19 ) of a patient, which support, together with a patient bed ( 35 ) can be moved into a passage ( 38 ) of a magnetic resonance tomograph. Driven by a motor, the support ( 14, 17 ) can be swivelled about at least one axis ( 33, 34 ) inside the passage ( 38 ) of the magnetic resonance tomograph, and that the components of the support ( 14, 17 ) and its drive, which are disposed inside the passage ( 38 ) of the magnetic resonance tomograph, are made of non-ferromagnetic materials.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an apparatus for generating a passive movement of a patient in a magnetic resonance tomograph with a support for supporting at least one body part of a patient, which support together with a patient bed or the like can be moved into the passage of a magnetic resonance tomograph.

[0003] 2. The Prior Art

[0004] To provide for an optimum diagnosis of injuries and disorders of joints, such as the ankle joint, it is known to scan a patient or at least relevant body parts by means of a magnetic resonance tomograph (MRT) and to make a diagnosis on the basis of the images obtained. For this purpose, it is frequently required to position or to be able to move the body part concerned in different and defined ways as required. Therefore, apart from static instantaneous shots, static images have so far been produced in various joint positions. The joint positions are adjusted manually via a mechanism, and viewing the resulting images is effected by means of an image loop (cine-mode). However, this is particularly time-consuming and therefore can only be applied in individual cases. Thus the possibilities of a modern magnetic resonance tomograph, which also provides for very fast image recordings, are not utilized. Hence, the diagnostics frequently indispensable with a magnetic resonance tomograph, which can excellently represent both the osseous and the cartilaginous parts of the human body as well as its soft-tissue structures, is not being used optimally.

[0005] In addition, there is the disadvantage that despite this presently most modern form of diagnosis not all disorders or injuries and damages of the human body can be detected by static instantaneous shots, in particular as it has not been possible so far to make shots in movement in a sufficient quality. However, this impairs the clinical diagnostics, as thus the probability (sensitivity) to diagnose existing pathological findings with diverse structures is not yet optimally possible or partly not possible. In magnetic resonance tomography, in contrast to X-ray diagnostics, there have so far not been any firmly predefined and reproducible settings to provide for the representation of real-time movements.

[0006] This is in particular due to the fact that as a result of the strong magnetic field in a magnetic resonance tomograph, the use of conventional movement apparatuses is not possible. Conventional electromechanical motors, which are usually employed in movement apparatuses, consist of magnets and coils which in the strong magnetic fields (0.2-3 Tesla) of a magnetic resonance tomograph deflect particularly strongly and thus lead to image distortions, so-called image artefacts. Once such image artefacts occur, however, a proper diagnosis no longer is possible.

SUMMARY OF THE INVENTION

[0007] Therefore, it is an object of the invention to provide an apparatus which provides for a defined reproducible passive movement of a patient in a magnetic resonance tomograph without producing image distortions, i.e. image artefacts, which make a diagnosis impossible.

[0008] In accordance with the invention, this object is achieved in that driven by a motor, the support can be swivelled about at least one axis inside the passage of the magnetic resonance tomograph, and that the components of the support and its drive, which are disposed inside the passage of the magnetic resonance tomograph, are made of non-ferromagnetic materials. Due to this structure of the apparatus, the sensitivity of the magnetic resonance diagnostics with respect to the examination of joints is increased distinctly. Thus predefined continuous movements can be set and the movements can be reproduced, in order to be able to represent real-time images (online images). The apparatus allows a body part to move in the magnetic resonance tomograph within the full scope of movement, passively and as desired for the respective diagnostic situation. Since the diagnostic possibilities have thus been improved and expanded, suspected injuries and the like can be detected and verified far better than has so far been possible. Since the components used in the passage of the magnetic resonance tomograph are formed of non-ferromagnetic materials, the occurrence of image artefacts, which make a diagnosis more difficult, is reduced in addition.

[0009] It was determined that the occurrence of image artefacts can furthermore be prevented in that the drive for swivelling the support is effected by means of a piezoelectric motor.

[0010] Preferably, the drive for swivelling the support is controlled by a control unit, which is grounded and shielded from magnetic radiation. By means of the apparatus in accordance with the invention, the movements can therefore be adjusted electronically and automatically controlled from outside the room of the magnetic resonance tomograph in always the same exactly reproducible positions. The position between the body part to be examined and the magnetic resonance tomograph can remain unchanged during the entire diagnostic procedure. At the same time, however, it is for the first time possible to perform precisely defined movements controlled by motors during the imaging procedure. On the one hand, this allows the examining person to specifically take a certain shot, but on the other hand to represent the movement itself in the sense of a real-time shot. Beside the use of a piezoelectric motor for driving the support, it is also possible to use pneumatic or hydraulic drives for this purpose.

[0011] When the control unit is disposed outside the zone around the magnetic resonance tomograph, in which in operation the magnetic flux density is ≧0.2 Tesla, the function of the control unit is not impaired by the strong magnetic field of the magnetic resonance tomograph. At the same time, image artefacts caused by the control unit can be avoided.

[0012] The control of the support can further be improved in that the control unit is provided with at least one sensor, in particular with an optical encoder, for detecting the position of the support or of the motors.

[0013] To be able to avoid the occurrence of image artefacts, which make diagnosis more difficult, even more effectively, the control unit can be connected with the drive of the support and possibly with the sensors via grounded and shielded lines, which outside the passage of the magnetic resonance tomograph are provided with ferrites.

[0014] In accordance with another embodiment of the invention, the support when driven by a motor, can independently be swivelled about two axes. Thus, the physiological movements of the body parts to be examined can be represented even better.

[0015] The physiological movement of an ankle joint can be imitated particularly well with the apparatus in accordance with the invention when the support can be swivelled about a first horizontal axis and a second axis inclined with respect to the vertical by about 35° in the horizontal plane and by about 18° in the sagittal plane. This inclination of the second axis corresponds to the average geometrical axis of the lower ankle joint as determined by Van den Bogard.

[0016] The pressure forces acting on the ankle joint etc. for instance when running, can be imitated during the examination in the magnetic resonance tomograph in that there are provided means for fixing the at least one body part of the patient on the support, and that at least portions of the support can be moved relative to the fixing means. Preferably, the support can be moved pneumatically or hydraulically relative to the means for fixing the body part. In this way, a stepwise compression of the body part to be examined can occur, which likewise leads to a change in the configuration of the individual parts of the body, which imitate the loads acting for instance when running or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which disclose several embodiments of the present invention. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention.

[0018] In the following the invention will be explained in detail by means of embodiments and with reference to the attached drawings, in which:

[0019]FIG. 1 shows a longitudinal section through the passage of a magnetic resonance tomograph with an apparatus in accordance with the invention arranged on a patient bed;

[0020]FIG. 2 shows a sectional view of the apparatus vertical to the sectional plane of FIG. 1; and

[0021]FIG. 3 shows a side view of the apparatus as shown in FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0022] The apparatus represented in the drawings is provided for use in a magnetic resonance tomograph (MRT) for instance with a magnetic flux density between 0.2 and 3.0 Tesla. The magnetic resonance tomograph is indicated in FIG. 1 by its passage 38. In the illustrated embodiment, the apparatus is arranged for examining the ankle joint. The apparatus has a support 14 for the heel of the foot and a support 17 for the sole of the foot disposed at an angle. The inner and outer malleoli of the foot are stabilized by side walls 15, whereas the support 17 for the sole of the foot is retained on a rear wall 16. In FIG. 1, the foot to be examined is indicated schematically by the reference numeral 19.

[0023] As shown in FIG. 1, the apparatus is mounted on a patient bed 35 by means of an indicated connecting unit 30. Together with the patient bed 35, a patient lying on his or her back can be moved into the passage 38 of the magnetic resonance tomograph, the apparatus being disposed at one end of the patient bed 35. By means of buckles 18, the foot can be maintained fixed in the apparatus. The foot not to be examined can be placed on another support 29 and is not detected in the examination.

[0024] The apparatus disposed on the patient bed 35 furthermore comprises two vertical side walls 1 and a vertical front wall 2 which merges into a horizontal front wall 3. On the side opposite the vertical front wall 2 a vertical rear wall 4 is provided, which is connected with a lower horizontal rear wall 5. Parallel, to the side walls 1 another vertical wall 6 extends, which by means of ball bearings 13 is articulated to the side walls 1 so as to be swivelled about a horizontal axis 33. The vertical walls 6 are connected with each other by a rear wall 11 and a V-shaped bottom wall 12.

[0025] In the V-shaped bottom wall 12, two recesses 27 are provided, which can receive a fastening unit 9. Via an intermediate part 8, the fastening unit 9 carries another fastening unit 10 with a gearwheel, on which there is mounted the support 14 for the heel as well as the rear wall 16 with the support 17 for the sole of the foot. The support 14 for the heel as well as the rear wall 16 with the support 17 for the sole of the foot can be rotated relative to the fastening unit 9 via the fastening unit 10. Due to the inclination of the V-shaped bottom wall 12 and the corresponding configuration of the fastening units 9 and 10, the support 14 for the heel with the rear wall 16 and the support 17 for the sole of the foot can be rotated about an axis 34 inclined with respect to the vertical by about 35° in the horizontal plane and by about 18° in the sagittal plane.

[0026] The fastening units 9 and 10 have associated thereto a piezoelectric motor 22, which carries a gearwheel 7 with conical tip for moving the fastening unit 10 relative to the fastening unit 9. Similarly, a piezoelectric motor 23 is provided at the vertical side wall 1, which carries a first gearwheel 24 which via another gearwheel 25 can be brought in engagement with a gearwheel 26, which is non-rotatably connected with one of the side walls 6. Driven by the motor 23, the side walls 6 can thus be swivelled relative to the side walls 1.

[0027] At the rear wall 16, a pressure valve unit 20 is disposed, by means of which the support 17 for the sole of the foot can be moved relative to the rear wall 16. There can thus be produced a continuously variable pressure acting on the sole of the foot.

[0028] In one of the side walls 1, two optical encoders 21 are positioned, which can detect the position of the side walls 6 relative to the side walls 1. Via lines not represented here, the data determined by the encoders 21 can be transferred to an electrobox 28, which in turn is connected with a control unit 32 via a shielded cable 36. The control unit 32 also actuates the motors 22 and 23 via shielded cables 37. Outside the passage 38 of the magnetic resonance tomograph, ferrite cores 31 are disposed on the shielded lines 36 and 37. The connection of the lines 36 and 37 with the control unit 32 is effected via likewise shielded cable connectors 39.

[0029] The materials used for the apparatus are not influenced by the magnetic field of the magnetic resonance tomograph. Therefore they produce no image artefacts which make a diagnosis impossible when non-ferromagnetic materials are used for the components disposed inside the passage 38 of the magnetic resonance tomograph. Such non-ferromagnetic materials include for instance VA4 stainless steel screws and threads, aluminum plates, pins, screws and air-pressure nozzles made of brass, plastic screws, and glass and ceramic ball bearings. The use of semifinished products made of polyoxymethylene (POM) is particularly favorable, as this plastic material absorbs the radiofrequency field (RF) and therefore generates no disturbing radiation.

[0030] The illustrated embodiment of the apparatus for generating a passive movement is particularly arranged for the examination of ankle joints. By means of the motors 22 and 23, the support 14 for the heel as well as the support 17 for the sole of the foot, which is connected with the rear wall 16, can be rotated such that the physiological movement of the ankle joint is imitated. By moving the support 17 for the sole of the foot relative to the rear wall 16 by means of the pressure valve unit 20, a weight load of the foot can be imitated in addition. It is thus possible to make both kinematic and static shots from different positions inside the passage 38 of the magnetic resonance tomograph for research and clinical routine diagnosis. As a result, these real-time shots of the movements considerably expand the possibilities for using a magnetic resonance tomograph known per se.

[0031] Accordingly, while a few embodiments of the present invention have been shown and described, it is to be understood that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention as defined in the appended claims. List of Reference Numerals 1. side wall 2. vertical front wall 3. horizontal front wall 4. vertical rear wall 5. horizontal rear wall 6. side wall 7. gearwheel with conical tip 8. intermediate part 9. fastening unit 10. fastening unit 11. rear wall 12. bottom wall 13. ball bearing 14. support (heel) 15. side wall 16. rear wall 17. support (sole of the foot) 18. buckle 19. foot 20. pressure valve unit 21. optical encoders 22. motor 23. motor 24. gearwheel 25. gearwheel 26. gearwheel 27. recess 23. electrobox 29. support 30. connecting unit 31. ferrite cores 32. control unit 33. horizontal axis x 34. vertical axis y 35. patient bed 36. shielded electric cables 37. shielded motor cables 38. MRT passage 39. cable connector 

What is claimed is:
 1. An apparatus for generating a passive movement of a patient in a magnetic resonance tomograph comprising a support (14, 17) for supporting at least one body part (19) of a patient, said support, together with a patient bed (35) can be moved into a passage (38) of a magnetic resonance tomograph, the support (14, 17) driven by a drive motor can be swivelled about at least one axis (33, 34) inside the passage (38) of the magnetic resonance tomograph, and components of the support (14, 17) and said drive motor, which are disposed inside the passage (38) of the magnetic resonance tomograph, are made of non-ferromagnetic materials.
 2. The apparatus as claimed in claim 1, wherein the drive motor for swivelling the support (14, 17) is comprised by at least one piezoelectric motor (22, 23).
 3. The apparatus as claimed in claim 1, wherein the drive motor for swivelling the support (14, 17) is controlled by a control unit (32), which is grounded and shielded from magnetic radiation.
 4. The apparatus as claimed in claim 3, wherein the control unit (32) is disposed outside a zone around the magnetic resonance tomograph, in which in operation magnetic flux density is ≧0.2 Tesla.
 5. The apparatus as claimed in claim 3, wherein the control unit (32) is provided with at least one sensor for detecting the position of the support (14, 17).
 6. The apparatus as claimed in claim 3, wherein the control unit (32) is connected with a drive (22, 23) of the support (14, 17) and with sensors (21) via grounded and shielded lines (36, 37) which outside the passage (38) of the magnetic resonance tomograph are provided with ferrites (31).
 7. The apparatus as claimed in claim 1, wherein driven by a motor, the support (14, 17) can be swivelled independently about two axes (33, 34).
 8. The apparatus as claimed in claim 7, wherein the support (14, 17) can be swivelled about a first horizontal axis (33) and about a second axis (34) inclined with respect to vertical by about 350 in a horizontal plane and by about 180 in a sagittal plane.
 9. The apparatus as claimed in claim 1, wherein there are provided fixing means (18) for fixing at least one body part (19) of a patient on the support (14, 17), and that at least portions of the support (17) can be moved relative to the fixing means (18).
 10. The apparatus as claimed in claim 8, wherein the support (17) can be moved in a manner selected from the group consisting of pneumatically and hydraulically relative to the fixing means (18) for fixing the body part (19). 